An ion selective electrode (ISE) is used for determining the quantity of an ion to be measured in a sample. For example, the ion selective electrode is immersed, together with a reference electrode, in a sample solution containing an electrolyte. In this state, a potential difference between the electrodes is measured to determine the quantity of the ion to be measured in the sample. Due to its simplicity, the ion selective electrode is widely utilized in analysis fields. In the medical field, the ion selective electrode is used for clinical test, and may be mounted not only in a dedicated machine for electrolyte concentration measurement but also in an automated clinical analyzer or a critical care analyzer as an electrolyte concentration measuring unit.
Particularly, high measurement accuracy is required in the medical field, and various measures have been devised to improve measurement accuracy. Generally, the ion selective electrode is a regularly replaced component, and its replacement is recommended after a certain number of times or a certain period of use. As a method for determining a defect or degradation of the ion selective electrode, Patent Literature 1 and Patent Literature 2 disclose methods of measuring the resistance value of the ion selective electrode.